# Electronic Devices and Circuits Questions and Answers – Approximate Hybrid Model and its use in CE, CB, CC

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Approximate Hybrid Model and its use in CE, CB, CC”.

1. What is the approximate hybrid parameter current gain of a CE amplifier?
a) -hfe
b) hfe
c) -hfc
d) hfc

Explanation: The current gain of a common emitter (CE) amplifier can be expressed in terms of approximate hybrid parameters. The current gain hfe is the forward transfer characteristics and is used to calculate the current gain in common emitter amplifiers.

2. What is the approximate hybrid parameter input resistance of a CE amplifier?
a) hoe
b) hib
c) hic
d) hie

Explanation: The input resistance of a common emitter (CE) amplifier can be expressed in terms of approximate hybrid parameters. The input resistance is universally expressed as hie. This is also the same for approximate as well as exact hybrid models.

3. What is the approximate hybrid parameter voltage gain of a CE amplifier?
a) hfe × RL / hie
b) -hfe × RL / hie
c) hfe × RL / hoe
d) -hfe × RL / hoe

Explanation: The voltage gain of a common emitter (CE) amplifier can be expressed in terms of approximate hybrid parameters. The voltage gain is equal to -hfe × RL / hie where, RL is load resistance, hie is input resistance and -hfe is the current gain.

4. What is the approximate hybrid parameter current gain of a CB amplifier?
a) -hfe / 1 + hfe
b) -hfe / 1 – hfe
c) hfe / 1 + hfe
d) hfe / 1 – hfe

Explanation: The current gain of a common base (CB) amplifier can be expressed in terms of approximate hybrid parameters. The current gain hfe is the forward transfer characteristics. The current gain of a common base amplifier is expressed as hfe / 1 + hfe.

5. What is the approximate hybrid parameter input resistance of a CB amplifier?
a) hfe / 1 – hfe
b) hfe / 1 + hfe
c) hie / 1 – hfe
d) hie / 1 + hfe

Explanation: The input resistance of a common base (CB) amplifier can be expressed in terms of approximate hybrid parameters. The input resistance is hie / 1 + hfe where, hie and hfe are the input resistance and current gain of CE amplifier respectively.
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6. What is the approximate hybrid parameter voltage gain of a CB amplifier?
a) hfe × RL / hie
b) -hfe × RL / hie
c) hfe × RL / hoe
d) -hfe × RL / hoe

Explanation: The voltage gain of a common base (CB) amplifier can be expressed in terms of approximate hybrid parameters. The voltage gain is equal to hfe × RL / hie where, RL is load resistance, hie is input resistance of CE amplifier and -hfe is the current gain of CE amplifier.

7. What is the approximate hybrid parameter current gain of a CC amplifier?
a) 1 + hoe
b) 1 – hoe
c) 1 + hfe
d) 1 – hfe

Explanation: The current gain of a common collector (CC) amplifier can be expressed in terms of approximate hybrid parameters. The current gain hfe is the forward transfer characteristics. The current gain of a common collector amplifier is expressed as 1 + hfe.

8. What is the approximate hybrid parameter input resistance of a CC amplifier?
a) hie – (1 + hfe) × RL
b) hie + (1 + hfe) × RL
c) hie – (1 + hfe) / RL
d) hie + (1 + hfe) / RL

Explanation: The input resistance of a common collector (CC) amplifier can be expressed in terms of approximate hybrid parameters. The input resistance is hie + (1 + hfe) × RLwhere, hie and hfe are the input resistance and current gain of CE amplifier respectively and RL is the load resistance.

9. What is the approximate hybrid parameter voltage gain of a CC amplifier?
a) 1 + hie × Ri
b) 1 – hie × Ri
c) 1 + hie / Ri
d) 1 – hie / Ri

Explanation: The voltage gain of a common collector (CC) amplifier can be expressed in terms of approximate hybrid parameters. The voltage gain is equal to 1 – hie / Ri where, Ri is equal to hie + (1 + hfe) × RL.

10. We use approximate hybrid models for transistors because they introduce less than 10% error.
a) True
b) False

Explanation: For the analysis of transistor amplifiers we use approximate hybrid models instead of exact hybrid models. They introduce less than 10% error which can be ignored since hybrid parameters themselves are not steady but vary considerably for the same type of transistor.

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